(LifeWire) -- On a blustery January day, a few tourists gather at the spot where the World Trade Center once stood in New York City. In pictures, words and a roll call of the dead, an area of kiosks and signs near the eastern edge of the site recounts the events of September 11, 2001.

Inge Oppenheimer (left), a Holocaust survivor from New York City, leaves the crematorium at the Auschwitz concentration camp in Poland.

These days, the 16-acre hole in the ground -- known to the world as ground zero -- is partially obscured by tall mesh-wire fences that surround a busy construction site. Yet one visitor is visibly moved by a photo taken during a fireman's funeral, one of the many images found on the information panels.

"I feel a little ashamed to be so curious," says Esther Winter, a tourist from Ringsted, Denmark, "but we watched it on television and were so shocked. I had to come here and get the feeling."

Like Winter, many visitors to New York City now include a trip to the World Trade Center site on their agenda. In 2006, more than 5.6 million toured the downtown site, a figure expected to double once the WTC memorial and museum are completed in 2010. Ground zero is just one of many destinations for "grief tourism," a relatively new term for an age-old human inclination -- that of traveling to and bearing witness at the sites of terrible or tragic events.

Confronting reality

Why are people drawn to sites of inexplicable horror or tragedy?

"People need to confront the reality of a disaster," says Dr. Grace Bellotti, a Bronx-based psychiatrist with the New York University Department of Psychiatry. "It's so unbelievable they need to go and look for themselves.'"

For some, the journey is intensely personal. "It was unbearable," Holocaust survivor Sol Rosenkranz, 90, of New York City, says of his trip five years ago to the Treblinka concentration camp in Poland, where his mother, brother, two sisters and sister-in-law perished.

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"I would never have gone but for my children," said Rosenkranz. "I wanted them to see where I came from, what I saw with my own eyes. I saw people going to their deaths. I lost my family. It was just impossible."

Of his immediate family, only Rosenkranz and one brother survived the Holocaust, Rosenkranz says. The family, originally from Krosniewice, Poland, had seen their father seized from their home by Nazi soldiers. They never saw him again. Rosenkranz himself was shuttled to six different camps, including Germany's Buchenwald, between 1942 and the end of the war.

For Inge Oppenheimer, 78, also of New York City, who was 12 when she and her family were deported from Cologne, Germany, to the concentration camp at Terezin, in the modern-day Czech Republic, revisiting the site in 2006 was unreal, like an "out-of-body experience." Unlike Rosenkranz's family, Oppenheimer and both of her parents survived internment.

"My grandchildren wanted to know more about their grandparents' lives, and being there was painful but helpful," says Oppenheimer, who also visited Auschwitz in Poland. "They were shocked, particularly at Auschwitz. They saw the barracks there. For them it was quite an experience."

People who have suffered or lost loved ones under terrible circumstances return time and again to mourn and "master the trauma," Bellotti says. "When we're hurt, when we have a loss, we have deep emotional feelings. The more you connect, the more you are able to master the trauma and cathect, transform or release the angry, anxious feelings."

The search for understanding

For many travelers, visiting a place of colossal tragedy -- like the Killing Fields of Cambodia, the Hiroshima Peace Memorial in Japan or even the flood-ravaged Ninth Ward of New Orleans -- can be an essential and enlightening element in understanding a place's history and culture. Sites where famous people were killed, like Dealy Plaza in Dallas, where President John F. Kennedy was assassinated -- hold similar sway.

"The 19th and 20th centuries created events that revealed the darkest side of humanity, and left the survivors resolved to tell the story," says Stephen Feinstein, director of the Center for Holocaust and Genocide Studies at the University of Minnesota. "With this has come a new respect for memorialization -- whether it be in a physical place, an artwork, a book, film or even college course. Some societies understand it as a process of mourning and as a reminder, as Robert Frost said, of the road not taken."

For others, the term "grief tourism" doesn't fully embrace the objectives of many memorials. "We are a memorial, yes, but at the same time we have an enormous and vibrant educational program," says Arthur Berger, senior adviser of external affairs at the U.S. Holocaust Memorial Museum in Washington, D.C. "We use the Holocaust not just as an example, but as a means to go from memory to action -- how to use the lessons of that awful period to prevent it from happening again."

Some of the most powerful memorials are unreconstructed remnants of the horrors that occurred. At Pol Pot's Tuol Sleng S-21 secret prison in Cambodia, where thousands were tortured and killed between 1975 and 1979, shelves are littered with skulls, and buildings remain untouched except for walls filled with black-and-white photographs of people who died there.

"The bottom line is that tourism to sites of memory should not be commercial, and maybe not religious either -- just a reminder of what man can do to mankind," Feinstein says.E-mail to a friend

LifeWire provides original and syndicated lifestyle content to Web publishers. Alexis Lipsitz Flippin is a writer and editor living in New York City and a former senior editor at Frommer's.